This invention relates to a process and an apparatus for dry spinning synthetic polymers, in which the yarns are blasted with hot gas be means of a blasting apparatus, radially from the inside to the outside below an annular spinning nozzle.
When dry spinning polymers, such as acrylonitrile polymers, polyurethane and aromatic polyamides, the hot spinning solution is normally forced through the bores of the spinning nozzle in a spinning shaft charged with hot gas. The solvent is thereby evaporated from the yarns.
It is important that the solvent is evaporated as quickly as possible, so that the yarns do not adhere due to too high a solvent content, when they beat against each other, this taking place particularly when the spacings between the holes on the nozzle are very small and the circulation of air in the shaft is unstable.
The hot spinning gas is at present normally blasted or blown in at the upper end of the spinning position above the spinning nozzle via screens and air filters and flows through the heated shaft in the direction in which the yarn is drawn off, the solvent being evaporated from the yarns and the gas being cooled. The gas enriched with solvent is drawn off by suction at the lower end of the shaft.
In this parallel flow of the hot spinning gas, the yarns which are removed further from the flow of gas, are not dried fast enough and show high fault rates owing to adhesion, as well as thick and thin regions.
A contrastingly improved apparatus for dry spinning is described in U.S. Pat. No. 3,737,508, in which some of the spinning gas, which is fed in parallel to the running direction of the yarns outside an annular nozzle, is drawn off by suction through the inside of the annular nozzle by means of gas supply devices, so that this partial flow flows transversely from the outside to the inside through the yarns below the nozzle. The remainder of the spinning gas flows with the yarns through a heated spinning shaft and is drawn off by suction at the end thereof. This apparatus suffers from the disadvantage that the inner row of yarns are not dried sufficiently quickly and still has a large number of points of adhesion.
In DE-OS No. 1,760,377, this disadvantage is partially compensated for in that the inner solution yarns issue from the spinning nozzle at a relatively high temperature. The technical cost of this solution is, however, exceedingly high.
Moreover, the transverse flow from the outside to the inside suffers from the disadvantage that the gas velocity from the outside to the inside increases since the space existing for the flow of gas towards the inside becomes smaller and the solvent-containing yarns act as gas sources. This produces a more substantial mechanical stressing and deflection of the yarns, which are positioned closest to the inner suction region, adhesion and splitting again being produced at weak spots.